import java.util.Scanner;

public class TriangleArea {

	public static void main(String[] args) {

		Scanner input = new Scanner(System.in);
		
		float aX = input.nextFloat();
		float aY = input.nextFloat();
		float bX = input.nextFloat();
		float bY = input.nextFloat();
		float cX = input.nextFloat();
		float cY = input.nextFloat();
		
		input.close();
		
		float result = (aX * (bY - cY) + bX * (cY - aY) + cX * (aY - bY)) / 2;
		
		if (result < 0f) {
			
			result *= -1f;
		}
		
		System.out.println((int)result);
	}

}